1. Field of the Invention
The present invention relates to a driving method and apparatus for a liquid discharge head for use in printing as well as in manufacturing color filters, thin film transistors, light-emitting devices, DNA devices, and the like.
2. Related Background Art
A liquid discharge apparatus has begun to be used for producing printed materials as well as for a patterning process in manufacturing color filters, thin film transistors, light-emitting devices, DNA devices, and the like.
Photolithography is widely adopted for such an industrial patterning method. However, the photolithography requires many steps and the cost for devices is huge, while providing extremely low material-use efficiency. Meanwhile, offset printing has a limitation on use as an industrial patterning technique due to the precision thereof.
Under the circumstances, a patterning method using a liquid discharge head, which is also called ink jet method, has become popular. The ink jet method allows for direct plotting on a patterning portion, thereby providing extremely high material-use efficiency while requiring a small number of steps, which is a useful patterning technique with low running cost.
Well-known ink jet methods are of the Kyser type described in Japanese Patent Publication No. 53-12138 and of the thermal jet type disclosed in Japanese Patent Publication No. 61-59914 (U.S. Pat. No. 5,754,194).
A shear-mode ink jet method using a piezoelectric ceramic is disclosed in Japanese Patent Application Laid-Open No. 63-247051 (U.S. Pat. No. 4,879,568).
As shown in FIGS. 9A and 9B, an ink jet head (liquid discharge head) 500 incorporating a shear-mode pressure generating device includes a bottom wall 501, a top wall 502, and shear-mode actuator walls 503. Each of the actuator walls 503 is formed of a lower wall 507 which is bonded to the bottom wall 501 and which is polarized in the direction indicated by an arrow 511, and an upper wall 505 which is bonded to the top wall 502 and which is polarized in the direction indicated by an arrow 509. A pair of adjacent actuator walls 503 forms an ink flow path (pressure-applying portion) 506. An air chamber 508 formed of a gap containing no ink is provided between adjacent ink flow paths 506.
An orifice plate 512 having a nozzle 510 is bonded to one end of each ink flow path 506, and electrodes 513 and 514 are provided as metallized layers on both sides of each actuator wall 503. More specifically, each actuator wall 503 is provided with the electrode 514 on the side of the ink flow path 506, and is provided with the electrode 513 on the side of the air chamber 508. The electrodes 513 facing the air chamber 508 are connected to a control circuit 520 for supplying an actuator driving signal, while the electrodes 514 defining the ink flow path 506 are connected to a ground.
A voltage is applied by the control circuit 520 to the electrodes 513 beside the air chambers 508, thus causing the actuator walls 503 to produce shear strain deformation in the direction where the volume of the ink flow paths 506 increases.
For example, as shown in FIG. 10, when a driving voltage is applied to the electrodes 513 beside the air chambers 508, an electric field is generated in the actuator walls 505 and 507 in the directions orthogonal to the respective polarizations as indicated by arrows, thus causing shear strain deformation of the actuator walls 505 and 507 in the direction where the volume of the ink flow path 506 increases. Then, a pressure decreases in the ink flow path 506 including the vicinity of the nozzle 510, so that ink is dispensed from an ink common flow path (not shown) on an ink supply side.
If the hydrodynamic resonant frequency of the inside of the ink flow path 506 is indicated by Fr, an inverse thereof is indicated by Tr (=1/Fr), and the time during which the voltage is applied is set to Tr/2, resonance across the system can be used, thereby making the amount of deformation greater than the original amount obtained as shear strain (non-resonance).
The hydrodynamic resonant frequency Fr can be determined by electric measurement using a well-known impedance measurement device. FIG. 11 shows the relationship between the measurement data obtained by the impedance measurement device (the frequency dependency of impedance) and the hydrodynamic resonant frequency Fr.
After the lapse of the voltage-applying time Tr/2, the voltage applied to the electrodes 513 beside the air chambers 508 is reset to zero. Then, the actuator walls 505 and 507 are deformed so that the ink flow path 506 may contract more than the normal state where the actuator walls 505 and 507 are not deformed and form a straight flow path, thus causing ink to be pressurized. This allows the ink to flow into the nozzles 510, and ink droplets are expelled from the nozzles 510.
In conventional ink ejecting apparatuses of this type, the volume of an ink droplet to be ejected depends upon the shape of an ink flow path, a driving voltage, and the like. Therefore, the shape of an ink flow path and the driving voltage are determined so that desired volume of an ink droplet can be obtained. If an ink jet apparatus is used as an industrial plotter, however, there are demands for high-definition ink jet performance, and for shorter plotting time. In order to shorten the plotting time, it is necessary to reduce the number of pulses required for plotting as much as possible. For higher definition, the pitch of an ink flow path is made narrower, thereby increasing the definition. In order to narrow the pitch of an ink flow path, in view of the limitation of machining, the thickness of a PZT (lead zirconate titanate) wall, which is a piezoelectric ceramic wall and which can change the volume of the ink flow path, must be reduced, and the depth of the ink flow path must also be reduced. This further leads to a limitation of driving voltage. Eventually, a high-definition head reduces the amount of deformation cause by the PZT wall, resulting in a reduced amount of discharge per dot.
On the other hand, Japanese Patent Publication No. 3-30506 (U.S. Pat. No. 4,563,689) describes that an additional pulse is applied before an application of the main pulse in order to determine the top position of ink meniscus in a nozzle, thereby controlling the volume of an ink droplet. By applying an additional pulse, the volume of an ink droplet can be slightly, but not significantly, increased.
Japanese Patent Application Laid-Open No. 2000-280463 describes a proposed method in which the volume of an ink droplet is increased by providing a pulse having a width of 0.30 T to 1.10 T as an additional emission (first emission) pulse before an application of a main emission (second emission) pulse, where T denotes the pulse width of the main emission pulse. In this method, two ink droplets are discharged to form one dot, thus making it possible to increase the volume of an ink droplet by a factor of up to about 1.5. However, it is difficult to further increase the amount of discharge.
As proposed in Japanese Patent Publication No. 6-55513 (U.S. Pat. No. 5,202,659), in order to increase the amount of discharge, a plurality of ink droplets which are sequentially ejected using a resonant frequency are combined in the air to control the volume of the ink droplets. With this approach, it can be expected that the volume of ink droplets sufficiently increases.
In an industrial ink jet apparatus, however, if the distance between a nozzle and a plotted base is extremely shortened in order to increase the deposition precision, a plurality of liquid drops are not combined in the air, but reach the base individually. In other words, there occurs a time lag in ink droplets to be applied for one-dot plotting, causing the reached drops do not form perfect circles, resulting in a failure of deposition precision.
Accordingly, it is an object of the present invention to provide a driving method and apparatus for a liquid discharge head in which the volume of a liquid drop can increase and the drop can reach with high precision even if the distance between a head nozzle and a plotted base is short.
It is another object of the present invention to provide a driving method and apparatus for a liquid discharge head which are also suitably used for an industrial patterning apparatus.
In order to achieve the above-mentioned object, according to a gist of the present invention, there is provided a driving method for a liquid discharge head including: a discharge port for discharging liquid; a pressure-applying portion communicating with the discharge port, for applying a pressure for discharge to the liquid; and a pressure generating device for generating the pressure, the method including a step of applying a first discharge pulse for discharging liquid and a second discharge pulse for discharging liquid to the pressure generating device in a sequential manner in response to an instruction of one-dot discharge, in which the pulse width of the first discharge pulse, the pulse width of the second discharge pulse, and a rest time between the first discharge pulse and the second discharge pulse are determined so that a first liquid discharged in response to the first discharge pulse has a volume equal to or greater than a second liquid discharged in response to the second discharge pulse and the discharge speed of the first liquid is lower than the discharge speed of the second liquid.
According to another gist of the present invention, there is provided a driving apparatus for a liquid discharge head including: a discharge port for discharging liquid; a pressure-applying portion communicating with the discharge port, for applying a pressure for discharge to the liquid; and a pressure generating device for generating the pressure, the apparatus including a driving circuit for applying a first discharge pulse for discharging liquid and a second discharge pulse for discharging liquid to the pressure generating device in a sequential manner in response to an instruction of one-dot discharge, in which the pulse width of the first discharge pulse, the pulse width of the second discharge pulse, and a rest time between the first discharge pulse and the second discharge pulse are determined so that a first liquid discharged in response to the first discharge pulse has a volume greater than a second liquid discharged in response to the second discharge pulse and the discharge speed of the first liquid is lower than the discharge speed of the second liquid.
According to still another gist of the present invention, there is provided a liquid discharge apparatus including: a liquid discharge head having: a discharge port for discharging liquid; a pressure-applying portion communicating with the discharge port, for applying a pressure for discharge to the liquid; and a pressure generating device for generating the pressure; a driving circuit for applying a first discharge pulse for discharging liquid and a second discharge pulse for discharging liquid to the pressure generating device in a sequential manner in response to an instruction of one-dot discharge; and a support for supporting a liquid-receiving member for receiving the liquid, in which the pulse width of the first discharge pulse, the pulse width of the second discharge pulse, and a rest time between the first discharge pulse and the second discharge pulse are determined so that a first liquid discharged in response to the first discharge pulse has a volume greater than a second liquid discharged in response to the second discharge pulse and the discharge speed of the first liquid is lower than the discharge speed of the second liquid, and in which a position of the liquid discharging head and a position of the support are determined so that the first liquid and the second liquid are combined to be applied to the liquid-receiving member.
According to the present invention, the first and second liquid drops are combined in a short discharge range, thus allowing the combined larger droplet to reach a liquid-receiving member with high precision.
In the present invention, the pulse width T1 and the pulse width T2, and the rest time K12 may be determined based on the hydrodynamic resonant frequency of the liquid discharge head. This enables liquid drops to be most effectively applied to the liquid-receiving member.
Also, according to another gist of the present invention, there is provided a driving method for a liquid discharge head including: a discharge port for discharging liquid; a pressure-applying portion communicating with the discharge port, for applying a pressure for discharge to the liquid; and a pressure generating device for generating the pressure, the method including a step of applying a first discharge pulse for discharging liquid and a second discharge pulse for discharging liquid to the pressure generating device in a sequential manner in response to an instruction of one-dot discharge, in which the following three equations are satisfied:
T1=k1xc3x97Nxc3x97Tr/2 
T2=k2xc3x97Tr/2 
K12=k3xc3x97(3Tr/4xe2x88x92T2/2), 
for k1, k2, and k3 each ranging from 0.9 to 1.1,
where N denotes an odd number more than one, Tr denotes an inverse of the hydrodynamic resonant frequency of the liquid discharge head, T1 denotes the pulse width of the first discharge pulse, T2 denotes the pulse width of the second discharge pulse, and K12 denotes the rest time between the first discharge pulse and the second discharge pulse.
According to still another gist of the present invention, there is provided a driving apparatus for a liquid discharge head including: a discharge port for discharging liquid; a pressure-applying portion communicating with the discharge port, for applying a pressure for discharge to the liquid; and a pressure generating device for generating the pressure, the apparatus including a driving circuit for applying a first discharge pulse for discharging liquid and a second discharge pulse for discharging liquid to the pressure generating device in a sequential manner in response to an instruction of one-dot discharge,
wherein the following three equations are satisfied:
T1=k1xc3x97Nxc3x97Tr/2 
T2=k2xc3x97Tr/2 
K12=k3xc3x97(3Tr/4xe2x88x92T2/2), 
for k1, k2, and k3 each ranging from 0.9 to 1.1,
where N denotes an odd number more than one, Tr denotes an inverse of the hydrodynamic resonant frequency of the liquid discharge head, T1 denotes the pulse width of the first discharge pulse, T2 denotes the pulse width of the second discharge pulse, and K12 denotes the rest time between the first discharge pulse and the second discharge pulse.
According to the present invention, the second liquid drop has a slightly smaller volume than that of the first liquid drop, while increasing the discharge speed of the liquid drops. Thus, two liquid drops can be combined in a short discharge range.
Also, according to the present invention, it is preferable that the driving circuit applies a non-discharge pulse, in response to which liquid is not discharged, subsequently to the second discharge pulse, and the following equations are satisfied:
T3=k4xc3x97Tr/2 
K23=k5xc3x97(3Tr/2xe2x88x92T2/2xe2x88x92T3/2), 
for k4 ranging from 0.2 to 0.5 and k5 ranging from 0.9 to 1.1,
where T3 denotes the pulse width of the non-discharge pulse, and K23 denotes the rest time between the second discharge pulse and the non-discharge pulse.
In this case, vibration, which is often large up to now, after discharging a liquid drop, can immediately be suppressed.
Also, according to the present invention, it is preferable that there is provided a driving signal including the first discharge pulse and the second discharge pulse to liquid discharge heads, the liquid discharge heads forming a liquid discharge head group having a plurality of the discharge ports, a plurality of the pressure-applying portions, and a plurality of the pressure generating devices, in which the pulse width of the first discharge pulse, the pulse width of the second discharge pulse, and the rest time have the same value.
In this case, there is no need for optimizing a pulse train for each liquid discharge head. Therefore, liquid discharge heads having some non-uniform discharge characteristics due to fluctuation in production would successfully be driven.
Further, according to another gist of the present invention, there is provided a driving method for a liquid discharge head including: a discharge port for discharging liquid; a pressure-applying portion communicating with the discharge port, for applying a pressure for discharge to the liquid; and a pressure generating device for generating the pressure, the method including a driving circuit for applying a first discharge pulse for discharging liquid and a second discharge pulse for discharging liquid to the pressure generating device in a sequential manner in response to an instruction of one-dot discharge, in which the following three equations are satisfied:
T1 greater than Tr 
T2=T1/N 
K12=3T1/2Nxe2x88x92T2/2, 
where N denotes an odd number more than one, Tr denotes an inverse of the hydrodynamic resonant frequency of the liquid discharge head, T1 denotes the pulse width of the first discharge pulse, T2 denotes the pulse width of the second discharge pulse, and K12 denotes the rest time between the first discharge pulse and the second discharge pulse.
Also, according to still another gist of the present invention, there is provided a driving apparatus for a liquid discharge head including: a discharge port for discharging liquid; a pressure-applying portion communicating with the discharge port, for applying a pressure for discharge to the liquid; and a pressure generating device for generating the pressure, the apparatus including a driving circuit for applying a first discharge pulse for discharging liquid and a second discharge pulse for discharging liquid to the pressure generating device in a sequential manner in response to an instruction of one-dot discharge, in which the following three equations are satisfied:
T1 greater than Tr 
T2T1/2 
K12=3T1/2Nxe2x88x92T2/2, 
where N denotes an odd number more than one, Tr denotes an inverse of the hydrodynamic resonant frequency of the liquid discharge head, T1 denotes the pulse width of the first discharge pulse, T2 denotes the pulse width of the second discharge pulse, and K12 denotes the rest time between the first discharge pulse and the second discharge pulse.
According to the present invention, the second liquid drop has a slightly smaller volume than that of the first liquid drop, while increasing the discharge speed of the liquid drops. Thus, two liquid drops can be combined in a short discharge range.
Also according to the present invention, it is preferable that the driving circuit applies a non-discharge pulse, in response to which liquid is not discharged, subsequently to the second discharge pulse, and the following equations are satisfied:
T3 less than Tr/2, 
K23=3T1xc3x97Nxe2x88x92T2/2xe2x88x92T3/2, 
where T3 denotes the pulse width of the non-discharge pulse, and K23 denotes the rest time between the second discharge pulse and the non-discharge pulse.
Also in this case, vibration, which is often large up to now, after discharging a liquid drop, can immediately be suppressed.